Maybe pressure balancer going bad or you don't have a pressure balanced valve

Valve stem seals? Either you change the valve stem, or you change the valve core. Depends on where your air is leaking from. If it's the valve core, you simply take a valve core removal tool or pocket screwdriver with a valve core removal end (either one can be had cheaply at an auto parts store), uncscrew the old valve core out, insert the new valve core, and tighten it in. If you're replacing the entire valve stem, best to let a tire shop do this, as your tire will have to be dismounted, remounted, and balanced again.

Valve stem seals? Either you change the valve stem, or you change the valve core. Depends on where your air is leaking from. If it's the valve core, you simply take a valve core removal tool or pocket screwdriver with a valve core removal end (either one can be had cheaply at an auto parts store), uncscrew the old valve core out, insert the new valve core, and tighten it in. If you're replacing the entire valve stem, best to let a tire shop do this, as your tire will have to be dismounted, remounted, and balanced again.

A stuck or worn balancing spool in a pressure balanced valve.